Magnetic-assisted electrochemical detection of Pb 2+ and Cd 2+ in Vietnamese seafood using Fe 3 O 4 @UiO-66-Py/rGO

Heavy metal contamination in seafood is a major concern for public health and export trade in Vietnam. In this work, a novel magnetic-assisted electrochemical sensor based on the Fe₃O₄@UiO-66-Py/rGO nanocomposite is developed for the ultra-trace detection of Pb²⁺ and Cd²⁺ in shrimp and fish samples. The binary composite combines the selective binding property of pyridine linkers (UiO-66-Py), the magnetic recovery of Fe₃O₄ nanoparticles, and the electrical conductivity of rGO to obtain ultra-low detection limits (LDs) in the range of ppb. Differential pulse anodic stripping voltammetry (DPASV) on a glassy carbon electrode (GCE) modified with the nanocomposite exhibited LODs for Pb²⁺ and Cd²⁺ of 0.3-0.4 ppb, with a broad linear range (1-200 ppb) and good selectivity. DFT calculations further elucidated the binding mechanism by calculating binding energies and identifying the optimal coordination structure for the bound metal ions on pyridine sites, thereby corroborating the experimental selectivity. Recovery tests (92-102%) on real Vietnamese seafood samples exhibited excellent correlation to ICP-MS results (R² > 0.98), confirming the feasibility of this technique for on-site detection at an aquafarm.